01 - Slice each chicken breast in half horizontally to create 4 thin fillets for even cooking.
02 - Whisk buttermilk, garlic powder, onion powder, salt, and pepper in a bowl. Add chicken and marinate for at least 15 minutes, up to 4 hours refrigerated for optimal flavor.
03 - Prepare three shallow bowls: one with flour, one with beaten eggs, and one with panko breadcrumbs mixed with grated Parmesan cheese.
04 - Remove chicken from marinade. Dredge each piece in flour, dip in egg mixture, then coat thoroughly in panko-Parmesan mixture, pressing gently to adhere.
05 - Heat ½ inch of vegetable oil in a large skillet over medium-high heat. Fry chicken pieces for 3-4 minutes per side until golden brown and internal temperature reaches 165°F. Drain on paper towels.
06 - Lightly toast brioche or sandwich buns until golden and warm.
07 - Spread Caesar dressing inside each bun. Layer with shredded romaine lettuce, crispy chicken fillet, additional dressing, shaved Parmesan, and freshly ground black pepper. Close sandwiches and serve immediately.